The present invention relates to an exposure apparatus and an original. The exposure apparatus of the present invention is suitable, for example, for an exposure apparatus that uses extreme ultraviolet (“EUV”) light for exposure light.
Currently, for manufactures of semiconductor devices, such as DRAMs and MPUs, a vigorous research and development has been performed for an implementation of a device having a design rule of a critical dimension (“CD”) of 50 nm or smaller. An exposure apparatus that utilizes EUV light (EUV exposure apparatus) is expected as a prospective exposure apparatus for this generation. In the EUV exposure apparatus, an optical path of the EUV light is maintained under the vacuum environment so as to prevent absorptions of the EUV light in the gas.
In general, a semiconductor exposure apparatus transfers onto a substrate (e.g., a wafer) a reduced size of a circuit patterned image of an original, such as a reticle or a mask, via a projection optical system. When a particle or a fine foreign matter adheres to a circuit patterned surface of the patterned surface of the reticle, an image of the particle is transferred each shot at the same position. The adhesion of the particle causes lowered yield of the semiconductor device manufacture and the degraded reliability of a semiconductor device itself.
As a solution for this problem, an exposure apparatus that uses a mercury lamp and an excimer laser for a light source arranges a transparent protection film called a pellicle apart from the reticle by several millimeters, and suppresses direct adhesions of particles onto a circuit patterned surface and transferring of particle images.
The pellicle has a thickness of about scores of nanometers to satisfy the transmittance required for the EUV exposure apparatus. This very thin pellicle cannot provide a sufficient strength mechanically or thermally. It is really difficult for the EUV exposure apparatus to prevent adhesions of particles using the pellicle that includes only a transparent protection film.
Prior art include, for example, Japanese Patent Laid-Open Nos. 2005-43895 and 2002-124463.
Japanese Patent Laid-Open No. 2005-43895 is insufficient in that use of a film having a thickness of about 30 nm to 300 nm for the pellicle remarkably lowers the transmittance to the EUV light (13.5 nm) down to about 50%, causing the lowered throughput. The pellicle film made of the above material is likely to oxidize and degrades its durability and handling easiness. Moreover, a wire mesh of 10 μm is used to support a film of 30 nm to 300 nm, and its manufacture would be extremely difficult. Even if it is applicable to a rectangular wind of 22 mm×8 mm used to separate the projection optical system space from the wafer stage space in the exposure apparatus, it appears to be difficult to manufacture the wire mesh that covers the entire reticle surface having a size of about 150 mm×150 mm. It is thus extremely difficult to put a filter wind for the EUV exposure apparatus proposed in Japanese Patent Laid-Open No. 2005-43895 to practical use as a pellicle.
Japanese Patent Laid-Open No. 2002-124463 is one conceivable solution for these problems but also insufficient. This reference uses a plane-parallel plate electrode only for the EUV light passing zone near the reticle to generate the electric field. It is possible to exclude incoming fine particle around the EUV light passing zone, but impossible to exclude particles that occur in other zones, such as particles that might occur when the reticle stage accelerates or decelerates in the reticle stage space. If the plane-parallel plate can generate the electric field throughout the reticle stage space, particles can be restrained in accelerating and decelerating the reticle stage. However, in that case, when the desired electric field of 33 kV/m in this specification is sought, the applied voltage of scores of kilovolts is needed, causing discharges and gas molecules sputtering, and finally increasing particles. Another embodiment illustrates use of a wire mesh, but the electric field occurs only between the reticle and the wire mesh in order to capture the electrons generated by the EUV light irradiations. Even if this wire is used to capture the particles, there are some particles that cannot be captured due to the polarity, and the wire is an insufficient restraining means.